Semiconductor technology has been progressing rapidly to the point where integrated circuits incorporating over a million transistors are possible. However, the rapid development of technologies, which require such integrated circuits, has increased just as rapidly. Applications such as real-time graphics, high-definition television, virtual reality, and other scientific and industrial applications are demanding higher speed, greater functionality, and even more rapid advances in very large-scale integrated circuit technology.
The demand for more functionality requires a tremendous increase in the number of transistors to be integrated onto a single integrated circuit chip. This requires shrinking the sizes of the transistors and/or having larger die sizes.
As the sizes of the transistors decrease, the resulting increased density requires an increasing number of interconnections within the integrated circuit chip. As the number of interconnections increases, the amount of area on the semiconductor die occupied by the interconnections becomes relatively large and may offset the savings made by reducing the size of the transistors.
A long sought goal in the semiconductor industry for very large-scale integrated circuits has been to achieve minimum area layouts for interconnections because minimum area layouts typically provide optimum performance and economy.
In addition, as the number of transistors proliferate, multiple levels of interconnections are required between the interconnect lines and the vias which connect different levels.
As everything is shrunk in size, misalignment comes to play a major factor in determining the performance capabilities of the interconnects. Unfavorable circumstances of misalignment can be fatal in the operation of an integrated circuit.
Further, it has been found that top misalignment between the uppermost interconnect line and a via has a great influence on via resistance and via chain yield. Small areas of line-via overlap, and incidents of via being corroded by etch clean solutions magnify the problems caused by misalignment.
Solutions to these problems have been long sought, but have equally as long eluded those skilled in the art.